1. FIELD OF THE INVENTION
This invention relates in general to the construction of breathing masks and in particular to a new and useful mask for use with compressed gas which includes an annular rim forming a seal cavity which is supplied with at least a portion of the compressed gas which escapes between the seal and the wearer's face into the interior of the mask.
2. DESCRIPTION OF THE PRIOR ART
The penetration of noxious substances into the interior space of a breathing mask must be prevented at the seal of the mask rim. The mask rim is to be designed so as to obtain a seat of the mask on the user's skin as comfortable as possible.
There are known protecting breathing masks having a double seal rim, in which the interspace between the seal rim is washed by exhaled air. Also protecting breathing masks having inflatable seals are known.
Another protecting breathing mask is known as disclosed in U.S. Pat. No. 3,167,070 in which, in order to insure an impeccable seal, the wall of the mask is provided with a dual seal rim. The inner seal rim is made of a porous material with closed cells which is impermeable for gas while the outer seal rim is made of a porous material having cells which are not tightly closed but rather provided with openings so that air and gas may pass therethrough. The interspace formed between the seal rims communicates, through a conduit and a gas filter, with a source of compressed air. An electrically driven air pump is used as the source of compressed air. A quantity of about 15 to 20 1/min of air is continuously pressed by the air supply device into the space between the two seal rims whereby a small overpressure is maintained in this space. Through the porous outer seal rim, air can continuously escape from the interspace to the outside and thereby prevent the penetration of noxious substances contained in the ambient air from entering into the space between the seal rims. This applies also in cases when, while using the protecting breathing mask, underpressure is produced in the interior of the mask during inhalation and air is taken into the interior of the mask from the space between the seal rims, if the seat of the inner gastight seal rim is not satisfactory. For operation, the known mask requires a source of compressed air in the form of an electrically driven pump, as well as electric energy. The wash air supplied through the pump must be purified in a filter before entering the space between the seal rims. There is no other way for preventing the endangering of the user. The expensively supplied and cleaned air escapes through the porous outer seal rim to the outside and is thus lost for the breathing.
There is further known a protecting breathing mask having a double seal rim and provided with an exhaling valve which is connected in parallel to the space between the two seal rims and opens directly to the open air and whose resistance is adjusted so that a part of the exhaling air flows directly into the peripheral space which communicates with the outside air through at least one outlet comprising a check valve. In this protecting breathing mask, the space between the two seal rims is practically permanently filled with exhaling air. Consequently, at any leakage between the seal rims and the skin surface of the user of the mask, only exhaling air is taken into the interior of the mask from the space between the seal rims, due to the underpressure produced by inhalation. The inmost seal rim may be designed as a seal lip extending in the direction of the space between the two seal rims. In spite of the two seal rims and the washing with the exhaling air this mask must be carefully adjusted. Even if the seal rim is designed as a seal lip, only the underpressure produced by inhalation can be used as the contact pressure and thereby seal pressure. To securely prevent the penetration of the outer air into the interior, the wash air volume and thus the space between the seal rims must be large.
In known smoke masks, an inflatable air tube is used for drilling the interspace between the rim of the mask and the user's head and sealing the interior of the mask against the outside air after being inflated. The inflation is effected by means of a small air pump communicating with the seal tube through a flexible tube extending through the interior of the mask. In this device, the seal tube after it is inflated has to provide for the sealing. It is recommended to use a neck strap in addition in order to prevent the seal tube from slipping off the user's face. The sealing is effected by contact pressure along a sealing line following the face. The seal tube is inflated by an additional, hindering device suspended from the mask and, moreover, it is necessary to permanently check if the contact pressure is sufficient for the sealing.